Look into using "PloP" boot manager (Really easy to boot from it) it's a "live CD" that allows you to boot from USB even if it's not an option in your bios. then use "UnetBootin" to "BURN" the .iso to a USB flash. it's worked for me numerous times.
Ill update with more info when i get home if needed. posting from work atm.
**windows instructions**
Edit:: for Distro why not give "Antix" a try, it's meant for older PC's and just installed it myself on some P3's yesterday Using the above boot method (boot to USB wasn't an option in the bios)
So what i did was burn the PloP .iso to a disc using imgburn
Then prepared my USB thumb drive, downloaded the Antix .iso from their website.
Opened UNetBootin, Chose the ISO radio button and pointed it to my downloaded iso.
Then Verified UnetBootin had the right thumb drive letter.
Click Go and wait for it to finish.
**unetbootin says you need to reboot, that's only if you're installing the *.iso on the host machine, if it's intended for another machine just unplug your drive**
Boot to the fresh burned disc (it's under 1.44 MB so even if your CD burner might be dying this should burn in enough time to hopefully not trigger the problem) **Also PloP can go on a floppy if your laptop & PC have a floppy drive (unlikely, i know)**
PloP boots, it's got cool space graphics and then lists all bootable options.
Choose USB. it scans all USB ports to find a USB drive with bootable properties, finds your antix thumb drive and boots to it.
Then Choose "Boot Antix" (this blue screen is what Unetbootin does, chose whatever option you want. CLI install is more for advanced users though)
When you're in the Live Antix environment there's an install option.
Antix is pretty sweet. it's got the icewm desktop, extremely close to like win 98. runs very well on these old P3's. my boss wanted me to load lightweight linux on them to donate to a daycare. Gonna load all the educational software I can find on it now! hopefully it inspires another little geek to the linux side.
PloP:
http://www.plop.at/en/bootmanager.html
UnetBootin:
http://unetbootin.sourceforge.net/